Method for measuring forces acted upon tire and apparatus for measuring forces acted upon tire

ABSTRACT

There is provided an apparatus for measuring forces acted upon a tire in which a radial force and a peripheral force acting to the tire, which are required for the high precision measurement of a friction coefficient on a road surface, are simply measured in a high precision by detecting a magnetic field formed by a magnet fixed to a tread portion of the tire by a magnetic sensor fixed to a rim and measuring the forces acting to the tire from a variant pattern of a magnetic flux density detected un the rotation of the tire and without influencing upon the balance of the tire, which contributes to the high precision measurement of the friction coefficient on the road surface.

TECHNICAL FIELD

This invention relates to a method for measuring forces acted upon atire for precisely measuring a friction coefficient on road surfacerequired in the control of an anti-skid brake system (hereinafterreferred to as ABS) or a traction control system of a vehicle.

BACKGROUND ART

In order to enhance performances of ABS used in the vehicle, it iseffective to conduct the control of lock-unlock at a state of a largefriction coefficient on road surface as far as possible. The frictioncoefficient on road surface is dependent upon a slippage ratio of awheel at a constant road surface state, so that ABS is designed so as tocontrol the lock-unlock in the vicinity of the slippage ratio giving amaximum friction coefficient on road surface.

In the conventional ABS, it is general to use a system that the slippageratio is determined by calculating from a speed of the vehicle and arotating speed of the wheel measured and the braking is automaticallycontrolled so as to enter this slippage ration into a given range.

However, the method of controlling the slippage ratio to obtain anoptimum friction coefficient on road surface is effective on a constantroad surface, but there is a problem in the actual running that even ifthe slippage ratio is controlled to the given range, the optimumfriction coefficient on road surface is not obtained because arelationship between the slippage ratio and the friction coefficient onroad surface is largely dependent upon the road surface material,weather and the like. For this end, it is desirable that forces of theroad surface acted upon a tire in a peripheral direction and a verticaldirection are measured and a friction coefficient is directly determinedfrom the measured forces and the braking is controlled so as to make thefriction coefficient measured optimum. Therefore, there is proposed amethod of directly measuring forces acted upon the tire as described,for example, in JP-A-10-506346.

According to this conventional method for measuring the forces, pluralpairs of magnet pair comprising two magnets arranged at two standardpoints, which are different in the position in a radial direction on thesame radius of a sidewall portion of the tire, are arranged so as toseparate apart from each other around a center axis of the tire, and amagnetic sensor is disposed and fixed to a vehicle at a radiallyposition corresponding to each of the standard points, and a timing ofdirectly facing the standard points relatively displacing with therotation of the tire to the magnetic sensors corresponding thereto isgotten as a timing of developing a peak of a magnetic flux detected bythe magnetic sensor, and relative displacement between the standardpoint in the magnet pair and relative displacement of the standard pointbetween the pair of the magnet pair are calculated from a time lag ofthe timing between these standard points, and strains of the tire in aperipheral direction and a vertical direction are calculated based onthese relative displacements, and forces acting to the peripheraldirection and vertical direction are determined from the calculatedstrains and the known tire rigidity.

However, this method is required to calculate the relative displacementfrom the time lag by taking data of the rotating speed of the wheelchanging at any time, so that there are problems that the controlbecomes complicated and the precision of the calculation is deterioratedby the influence of the precision on the rotating speed of the wheel.

The invention is made in the light of the above problems, and an objectthereof is to provide a method and an apparatus for measuring forcesacted upon a tire in which forces acted upon the tire in radialdirection and peripheral direction of the tire required for the highprecision measurement of friction coefficient on road surface can bemeasured simply in a high precision.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, the invention has the followingsummary and construction.

-   (1) The method for measuring forces acted upon a tire according to    the invention is a method for measuring at least one of forces in a    peripheral direction and a radial direction of a running tire    mounted onto a rim acted upon a ground contact face, in which when a    point on an outer peripheral face of the rim is Q and an intersect    between a straight line passing through the point Q under no action    of external force and extending in the radial direction and an inner    peripheral face of a tread portion of the tire is P, said forces are    determined from a variant pattern that a relative displacement of    the point P to the point Q in the peripheral direction or the radial    direction is changed in accordance with a rotating position of the    point Q when the point P passes through the ground contact portion    of the tire.-   (2) In the method for measuring forces acted upon the tire according    to the invention described in the item (1), a magnetic field formed    by a magnet arranged on one of the point P and the point Q is    continuously measured by a magnetic sensor arranged on the other of    the point P and the point Q, and the variant pattern of the relative    displacement between the point P and the point Q is determined by    reverse calculation from a variant pattern of a magnetic flux    density changed in accordance with the relative displacement.

Moreover, the “magnet” simply described throughout the specificationmeans things capable of forming any magnetic field. For example, themagnet includes a composite magnet in which plural magnets are arrangedin a given form, or a magnetic body magnetized in a given magnetizationdistribution.

-   (3) In the method for measuring forces acted upon the tire according    to the invention described in the item (2),-   the measurement of the magnetic flux density is conducted by using    the magnet arranged so that a magnetic force line distribution of    the magnetic field forms a plane symmetry with respect to a    meridional plane of the tire including the point P or the point Q    under no action of external force to the tire,    -   and the force acting in the peripheral direction of the tire is        determined from an average between maximum value and minimum        value of a variant pattern of a tire peripheral component in the        measured magnetic flux density and the force acting in the        radial direction of the tire is determined from a difference        between the maximum value and the minimum value of the variant        pattern.

Moreover, the “tire meridional plane” means a plane including arotational axis of the tire.

-   (4) In the method for measuring forces acted upon the tire according    to the invention described in the item (2), the measurement of the    magnetic flux density is conducted by using the magnet arranged so    that a magnetic force line distribution of the magnetic field forms    a plane symmetry with respect to a meridional plane of the tire    including the point P or the point Q under no action of external    force to the tire,    -   and the force acting in the radial direction of the tire is        determined from a maximum value or a minimum value of a variant        pattern of a tire radial component of the measured magnetic flux        density.-   (5) In the method for measuring forces acted upon the tire according    to the invention described in the item (2), the measurement of the    magnetic flux density is conducted by using the magnet arranged so    that a widthwise component of a magnetic flux density of the    magnetic field changes along the peripheral direction of the tire    under no action of external force to the tire,    -   and the force acting in the peripheral direction of the tire is        determined from an average between maximum value and minimum        value of a variant pattern of a tire widthwise component in the        measured magnetic flux density and the force acting in the        radial direction of the tire is determined from a difference        between the maximum value and the minimum value of the variant        pattern.-   (6) In the method for measuring forces acted upon the tire according    to the invention described in the item (2),-   the measurement of the magnetic flux density is carried out in    parallel with respect to a pair of magnets arranged near to each    other so that changes of widthwise components of magnetic flux    densities formed along the peripheral direction of the tire form a    reversal relation under no action of external force to the tire,    -   and when an average value of maximum values in a reversal        pattern reversed from a variant pattern of the magnetic flux        density of the tire widthwise component measured on one of the        magnets and in a variant pattern of the magnetic flux density of        the tire widthwise component measured on the other magnet is an        average maximum value and an average value of minimum values in        these patterns is an average minimum value, the force acting in        the peripheral direction of the tire is determined from an        average between the average maximum value and the average        minimum value, and the force acting in the radial direction of        the tire is determined from a difference between the average        maximum value and the average minimum value.

Moreover, instead of a feature that the force acting in the peripheraldirection of the tire is determined from the average between the averagemaximum value and the average minimum value and the force acting in theradial direction of the tire is determined from the difference betweenthe average maximum value and the average minimum value, the force inthe peripheral direction of the tire may be determined from an averageof a maximum value and a minimum value based on arithmetic addition ofthe reversal pattern on one of the magnets and the variant pattern onthe other magnet and the force acting in the radial direction may bedetermined from a difference between the maximum value and the minimumvalue.

-   (7) The apparatus for measuring forces acted upon a tire according    to the invention is an apparatus for measuring forces acted upon a    tire used in the measuring method described in any one of the items    (2)-(6),    -   which comprises a magnet arranged on an inner peripheral face of        a tread portion, and a magnetic sensor attached directly or        indirectly through a fitting jig to an outer peripheral face of        a rim.-   (8) The apparatus for measuring forces acted upon a tire according    to the invention is an apparatus for measuring forces acted upon a    tire used in the measuring method described in any one of the items    (2)-(6),    -   which comprises a magnet attached directly or indirectly through        a fitting jig to an outer peripheral face of a rim and a        magnetic sensor arranged on an inner peripheral face of a tread        portion.-   (9) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (7) or (8), the    magnet is constituted with a sheet-shaped magnet having magnetic    poles of the same polarity at both ends in a longitudinal direction    and a magnetic pole of a polarity opposite to the magnetic poles of    both the ends at a center in the longitudinal direction, and the    magnet is arranged so as to extend the longitudinal direction in a    peripheral direction of the tire.-   (10) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (7) or (8), the    magnet is constituted with two magnets each having magnetic poles of    opposite polarities at both ends, and these two magnets are extended    in opposite directions to each other in a widthwise direction of the    tire and arranged side by side in a peripheral direction of the    tire.-   (11) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (7), the magnet is    constituted with at least one sheet-shaped magnet in which    distributions of magnetization at front and back faces thereof form    a reversal relation to each other.-   (12) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (11), the    sheet-shaped magnet is constituted with a rectangular rubber sheet    of an even thickness in which the magnetization of the same polarity    at each of the front and back faces is distributed substantially    uniformly over a full face thereof.-   (13) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (12), the one    rectangular sheet-shaped magnet is arranged so as to position a    magnet center to the point P and direct a side of the magnet to a    peripheral direction.-   (14) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (12), four    rectangular sheet-shaped magnets having the same size are arranged    so as to position their magnet centers to apexes of a tetragon    having a center at the point P and one side parallel to a peripheral    direction of the tire, and a side of each of these magnets is    directed to the peripheral direction of the tire, and distances    separated between these magnets in the peripheral direction of the    tire and the widthwise direction of the tire are not more than 100    mm, respectively, and directions of magnetic poles of the    sheet-shaped magnets located at mutually adjacent apexes of the    tetragon having a center at the point P are opposed to each other.-   (15) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (12), two    rectangular sheet-shaped magnets having the same size are arranged    so as to position their magnet centers to a pair of apexes forming a    diagonal relationship of a tetragon having a center at the point P    and a side parallel to a peripheral direction of the tire, and a    side of each of these magnets is directed to the peripheral    direction of the tire, and distances separated between these magnets    in the peripheral direction of the tire and the widthwise direction    of the tire are not more than 100 mm, respectively, and directions    of magnetic poles of these sheet-shaped magnets are made the same.-   (16) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (12), six    rectangular sheet-shaped magnets having the same size are arranged    at three rows from side to side along a peripheral direction of the    tire in the same direction and at equal intervals every two magnets,    and a side of each of these magnets is directed in the peripheral    direction of the tire, and distances separated between these magnets    in the peripheral direction of the tire and in the widthwise    direction of the tire are not more than 100 mm, respectively, and    directions of magnetic poles of these six magnets are opposed to    each other even between the adjacent magnets in the peripheral    direction of the tire and in the widthwise direction of the tire,    -   and magnetic sensors are arranged on lines passing through        centers of two rectangles formed by mutually adjacent four        sheet-shaped magnets under no action of external force to the        tire and extending inward and outward in a radial direction in        correspondence to each of these rectangles.-   (17) In the apparatus for measuring forces acted upon a tire    according to the invention described in any one of the items (7) to    (16), the magnet or the magnetic sensor is indirectly attached to an    outer peripheral face of a rim through a fitting jig and at a    position separated outward from the outer peripheral face of the rim    in a radial direction of the tire.-   (18) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (17), the fitting    jig is a stay or an annular body going round the periphery of the    rim.-   (19) In the apparatus for measuring forces acted upon a tire    according to the invention described in the item (17) or (18), which    further comprises an adjusting means for adjusting a distance of the    magnet or the magnetic sensor separated from the outer peripheral    face of the rim, and an operating means for actuating the adjusting    means arranged inward in the radial direction of the tire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a tire showing a point on a tread portion anda direction of this point.

FIG. 2 is a graph showing a relation between peripheral component andradial component of a displacement of a point on a tread portion and adirection φ thereof.

FIG. 3 is a graph showing a relation between peripheral component andradial component of a displacement of a point on a tread portion and adirection φ thereof.

FIG. 4 is a section view of a tire used in a method for measuring forcesacted upon the tire according to a first embodiment of the invention.

FIG. 5 is a section view of a tire showing a section A1-A1 of FIG. 4.

FIG. 6 is a graph showing a relation between a change of a peripheralcomponent in a magnetic flux density and a direction φ.

FIG. 7 is a graph showing a relation between a change of a radialcomponent in a magnetic flux density and a direction φ.

FIG. 8 is a system constitution view illustrating a force measuringsystem for measuring forces by using the method for measuring forcesacted upon the tire according to the above embodiment.

FIG. 9 is a graph showing time changes of a peripheral component and aradial component in a magnetic flux density detected by a magneticsensor.

FIG. 10 is a section view of a tire used in a method for measuringforces acted upon the tire according to a second embodiment of theinvention.

FIG. 11 is a perspective view of a tire illustrating an arrangement ofmagnets.

FIG. 12 is a schematically developed view showing a tire widthwisecomponent of a magnetic flux density on an equator at the same height ina radial direction of the tire as that of a magnetic sensor.

FIG. 13 is a graph showing a relation between a change of a peripheralcomponent of a magnetic flux density and a direction φ.

FIG. 14 is a graph showing a time change of a peripheral component of amagnetic flux density detected by a magnetic sensor.

FIG. 15 is a section view of a tire used in a method for measuringforces acted upon the tire according to a third embodiment of theinvention.

FIG. 16 is a section view of a tire showing a section A2-A2 of FIG. 15.

FIG. 17 is a diagrammatic view showing a distribution of magnetic forcelines radiated from a sheet-shaped magnet.

FIG. 18 is a section view of a tire used in a method for measuringforces acted upon the tire according to a fourth embodiment of theinvention.

FIG. 19 is a perspective view illustrating an arrangement of magnets.

FIG. 20 is a diagrammatic view showing a distribution of magnetic forcelines radiated from a sheet-shaped magnet.

FIG. 21 is a schematically developed view showing a tire widthwisecomponent of a magnetic flux density on an equator at the same height ina radial direction of the tire as that of a magnetic sensor.

FIG. 22 is a section view of a tire showing a modification example ofthe fourth embodiment of the invention.

FIG. 23 is a perspective view of a tire illustrating an arrangement ofmagnets.

FIG. 24 is a diagrammatic view showing a distribution of magnetic forcelines radiated from a sheet-shaped magnet.

FIG. 25 is a schematically developed view showing a tire widthwisecomponent of a magnetic flux density on an equator at the same height ina radial direction of the tire as that of a magnetic sensor.

FIG. 26 is a section view of a tire used in a method for measuringforces acted upon the tire according to a fifth embodiment of theinvention.

FIG. 27 is a perspective view illustrating an arrangement of magnets.

FIG. 28 is a diagrammatic view showing a distribution of magnetic forcelines radiated from a sheet-shaped magnet.

FIG. 29 is a schematically developed view showing a tire widthwisecomponent of a magnetic flux density on an equator at the same height ina radial direction of the tire as that of a magnetic sensor.

FIG. 30 is a graph showing a relation between a change of a radialcomponent in a magnetic flux density and a direction φ.

FIG. 31 is a section view of a tire showing a modification example ofthe other embodiment of the invention.

FIG. 32 is a section view of a tire showing a section A3-A3 of FIG. 31.

FIG. 33 is a section view of a tire showing a modification example ofthe other embodiment of the invention.

FIG. 34 is a section view illustrating an embodiment of attaching amagnetic sensor.

FIG. 35 is a section view illustrating another embodiment of attaching amagnetic sensor.

FIG. 36 is a section view of a tire showing a section A4-A4 of FIG. 33.

FIG. 37 is a graph showing a correlation between measured values offorces in radial direction and peripheral direction of the tire measuredat given intervals over a time ranging from just before braking of avehicle to stop thereof, and calculated value determined from magneticmeasurement.

BEST MODE FOR CARRYING OUT THE INVENTION

The method for measuring forces acted upon a tire according to theinvention determines forces acted upon the tire from a time change ofdisplacement of a point P on a tread portion of the tire under therotation of the tire, and a principle thereof is described below. FIG. 1is a schematically front view of a tire explaining a displacement D in adirection φ of a given point P located on an inner peripheral face of atread portion 2 of a tire 1 at a center in a widthwise direction of thetire. The direction φ of the point P means that a coordinate componentin a peripheral direction of the tire at a position of the point Prepresented by a polar coordinate taking a tire rotational center O asan original point is shown by a given standard direction, for example, aperipheral angle from a direction φ just above an axis. The displacementD of the point P in the direction φ means a physical amount when thepoint P at a center of an inner peripheral face of the tread portion inthe direction φ defined in the tire 1 at a state of contacting noportion with a road surface, i.e. under no action of external forcemoves to a point P₁ under an action of external force to a groundcontact face of the tire by contacting the tire with the road surfaceand a difference of position between the point P and the point P₁ isshown by vector.

At first, it is considered a state that only a force R in a radialdirection of the tire is applied to the ground contact face of the tire1 and a force T in a peripheral direction of the tire is not applied ifit is intended to rotate the tire 1. In this state, when the point P isexistent in a zone ranging from a direction φ_(f1) to a direction φ_(b1)toward a direction CCW, the point P is not subjected to an influence offorce from the ground contact face and hence a magnitude of thedisplacement D is zero. On the other hand, when the point P is existentin a zone positioning on the ground contact face, i.e. a zone rangingfrom φ_(b2) to φ_(f2) toward the direction CCW, the ground contactingportion of the tire is pushed by the road surface to approach to thetire rotational center and widen in the peripheral direction, so that aradial component Dr of the displacement D of the point P is directedtoward the inside and becomes maximum when the point P locates at adirection φ_(d), while a peripheral component Dθ is zero when the pointP is the direction φ_(d), but when the point P is existent in otherdirections, a force of widening the ground contact face outward in theperipheral direction is acted to cause the displacement in such adirection. Further, the point P existing in a non-contact portion of thetire 1 adjacent to the ground contact face, i.e. zones ranging fromφ_(f2) to φ_(f1) and from φ_(b1) to φ_(b2) toward the direction CCW issubjected to an influence of a force acted to the ground contact face tocause the same displacement D as mentioned above.

FIGS. 2 a and 2 b are graphs showing a relation between peripheralcomponent Dθ and radial component Dr of displacement D and direction φ,in which an abscissa is the direction φ and an ordinate is componentsDθ, Dr, respectively. The positive and negative of each of thesecomponents are as follows. That is, as to the radial component Dr, adirection toward the tire rotational center is positive, and as to theperipheral component Dθ, the direction CCW toward anticlockwise rotationis positive. Also, the displacement D in case of assuming that a forcerotating the tire 1 is zero as mentioned above is shown by a curve T0 inFIGS. 2 a and 2 b.

In addition to the action of the force R in the radial direction of thetire shown by T0, when a torque rotating the tire 1 in a clockwisedirection is applied to the tire 1 to act a force T1 in the peripheraldirection of the tire from the road surface to the ground contact faceof the tire 1 in an anticlockwise rotation, the displacement D isrepresented by a curve T1 in FIGS. 2 a, 2 b, which is a value obtainedby adding the above displacement shown by the curve T0 with adisplacement of anticlockwise rotation produced over a whole of theground contact face resulted from the force T1 in the peripheraldirection of the tire. Moreover, when the force in the peripheraldirection of the tire is a value T2 larger than T1, the displacement Dis represented by a curve T2 in FIGS. 2 a, 2 b. From these facts, it isunderstood that the force T in the peripheral direction of the tireacting to the ground contact face of the tire hardly exerts an influenceon the radial component Dr of the displacement D, but increases ordecreases substantially uniformly the peripheral component Dθ of thedisplacement over the whole of the ground contact face, and the degreeof increase or decrease is proportional to the magnitude of the force Tin the peripheral direction of the tire.

The above is explained with respect to the influence of the force T inthe peripheral direction of the tire upon the displacement D of thepoint P. Then, an influence of a force R in the radial direction of thetire is considered. FIGS. 3 a and 3 b show changes of peripheralcomponent Dθ and radial component Dr in the displacement D of the pointP when the force R in the radial direction of the tire is changed at astate that the force T in the peripheral direction of the tire acting tothe tire 1 is zero, in which an abscissa is a direction φ and anordinate is each of the components Dθ, Dr in the displacement and curvesR0, R1, R2 correspond to cases that the force R in the radial directionof the tire acting to the tire is R0, R1 and R2, respectively, and themagnitude of the force R in the radial direction of the tire is smallestin R0 and largest in R2. As seen from FIGS. 3 a and 3 b, the peripheralcomponent Dθ and radial component Dr in the displacement of the point Pchange substantially in proportion to the magnitude of the force R inthe radial direction of the tire.

In summary, the peripheral component Dθ_(φ) and radial component Dr_(φ)of the displacement D in the direction φ can be represented by equations(1) and (2) using the force R in the radial direction of the tire andthe force T in the peripheral direction of the tire acting to the groundcontact face.Dθ _(φ) =M1(φ)·R+N1(φ)·T  (1)Dr _(φ) =M2(φ)·R+N2(φ)·T  (2)

In this case, M1(φ), N1(φ), M2(φ) and N2(φ) are proportional constantsdefined by the direction φ, respectively. As previously mentioned, thedisplacement Dr in the radial direction is hardly subjected to theinfluence of the force T in the peripheral direction, so that N2(φ) isapproximately zero.

If values Dθ_(φ1) and Dθ_(φ2) of Dθ with respect to specified twodirections φ1 and φ2 are gotten from the above, the force R in theradial direction of the tire and the force T in the peripheral directionof the tire can be calculated back according to the following equations(3) and (4) using M1(φ1), N1(φ1), M1(φ2) and N1(φ2) previouslydetermined by experiments or the like, and also if value Dr_(φ3) of Drwith respect to a specified direction φ3 is gotten, the force R in theradial direction of the tire can be calculated back according to thefollowing equation (5) using M2(φ3) previously determined by experimentsor the like.R=(N1(φ2)·Dθ _(φ)1−N1(φ1)·Dθ _(φ2))/MM   (3)T=(M1(φ1)·Dθ _(φ2) −M1(φ2)·Dθ _(φ1))/MM   (4)R=Dr _(φ3) /M2(φ3)  (5)provided that MM=(M1(φ1)·N1(φ2)−M1(φ2)−N1(φ1))  (6).

In the above explanation, the displacement D of the point P is definedas a deviance from a phantom position under no action of external forceproduced by the action of external force, but the measurement thereof ispractically difficult. For this end, a point that a relativedisplacement to the phantom position is zero even if the tire is rotatedunder the action of external force, i.e. a relative displacement to apoint Q on a rim capable of approximating as a rigid body is measuredinstead of the deviance of the point P from the phantom position,whereby the displacement of the point P can be determined. Therefore,the “displacement D of the point P” in the above explanation can berephrased to “relative displacement to point Q on the rim”. As the pointQ is taken a point on an outer peripheral face of the rim located at thesame radius of the point P, at where a sensor detecting the displacementof the point P can be arranged.

The invention determines the force R in the radial direction of the tireand the force T in the peripheral direction of the tire acted upon thetire from the above-measured displacement Dθ_(φ or Dr) _(φ) in the givendirection φ using the known modulus of elasticity. In all of thefollowing embodiments, the force R or T acted upon the tire isdetermined by magnetically measuring displacement Dθ or Dr.

A first embodiment is described with reference to FIGS. 4-9. FIG. 4 is aview showing a section of a tire 1 at a meridional plane of the tire,and FIG. 5 is a section view corresponding to an arrow A1-A1 of FIG. 4.To a widthwise central portion of an inside face of a tread portion in aradial direction of the tire or an inner peripheral face of the tire isattached one rectangular sheet-shaped magnet 4, while a magnetic sensor8 is fixed to a widthwise central portion of an outside face of a rimwell portion 6A of a rim 6 in the radial direction of the tire. Themagnet 4 is arranged so as to extend a longitudinal direction of therectangle into a peripheral direction of the tire and to position acenter of the rectangle to a point P on the inner peripheral face of thetire on a straight line L passing through a center of a detectingportion of the magnetic sensor 8 and extending inward and outward in theradial direction of the tire. An apparatus 10 for measuring forces actedupon the tire is constituted with the magnet 4 and the magnetic sensor8.

The magnetic sensor 8 is comprised of a sensor 8A detecting a radialcomponent Hr of a magnetic field emitted from the magnet 4 and a sensor8B detecting a peripheral component Hθ. To the rim 6 is attached atransmitting device 7 for treating signals input from the magneticsensor 8 through a junction line and a connector (not shown) andtransmitting to a receiving device disposed on a vehicle body.

At both ends of the magnet 4 extending into the peripheral direction ofthe tire are formed magnetic poles of the same polarity and a magneticpole of a polarity opposite to those of both the ends is formed at acentral portion in the longitudinal direction. In the illustratedembodiment, for example, magnetic poles 4S of S-pole are formed at boththe ends and a magnetic pole 4N of N-pole is formed at the centralportion. According to the magnet having such a construction, a magneticfield is formed so that a magnetic force line distribution forms a planesymmetry with respect to a meridional plane including the point P or aplane including the straight line L and perpendicular to paper in FIG.5.

In the above apparatus 10 for measuring forces acted upon the tire, whenforce is applied to a ground contact face of the tire 1 to cause theaforementioned displacement D in the point P attached with the magnet 4,a relative position of the magnetic pole 4N to the magnetic sensors 8A,8B fixed to the rim 6 also changes only by the displacement D, and as aresult, peripheral component Hθ and radial component Hr of the magneticfield formed by the magnet 4 to be detected by the magnetic sensors 8A,8B change.

When the displacement D of the point P is zero, the magnetic force linesdirect into the radial direction at the positions of the magneticsensors 8A, 8B, so that Hθ is zero and Hr becomes a given value Hr0, andhence changes ΔHθ and ΔHr of peripheral component Hθ and radialcomponent Hr of magnetic flux density after the displacement of thepoint P to those before the displacement can be represented by thefollowing equations:ΔHθ=Hθ=A1·Dθ+B1·Dr  (7)ΔHr=Hr0−Hr0=A2·Dθ+B2·Dr  (8)wherein A1, B1, A2 and B2 can be approximated as a constant because theyare not large in the displacement.

The magnetic sensors 8A, 8B are disposed on the straight line L oppositeto the front of the magnetic pole 4N, so that the displacement of themagnetic pole 4N approaching to or separating apart from the magneticsensors 8A, 8B along the straight line L, or the peripheral component Hθof the magnetic flux density is hardly influenced even if Dr increasesor decreases, and also the displacement moving the magnetic pole 4N onthe periphery of the same radius into the peripheral direction, orradial component Hr of the magnetic flux density at the magnetic sensors8A, 8B is hardly influenced even if Dθ increases or decreases, and henceA2 and B1 in the above equations can be approximated to zero. As aresult, they can be represented by the following equations (9) and (10):ΔHθ=A1·Dθ  (9)ΔHr=B2·Dr  (10)

As seen from the equations (9) and (10), ΔHθ is proportional to Dθ andΔHr is proportional to Dr, so that graphs showing dependencies of ΔHθand ΔHr to force R in the radial direction and force T in the peripheraldirection from FIGS. 2, 3 are shown in FIGS. 6 and 7, respectively.FIGS. 6 a and 6 b are graphs showing dependencies of a change ΔHθ of theperipheral component of the magnetic flux density upon the force R inthe radial direction when the force T in the peripheral direction iszero and upon the force T in the peripheral direction when the force rin the radial direction is a constant value R0, respectively, and FIGS.7 a and 7 b are graphs showing dependencies of a change ΔHr of theradial component of the magnetic flux density upon the force R in theradial direction when the force T in the peripheral direction is zeroand upon the force T in the peripheral direction when the force R in theradial direction is a constant value R0, respectively.

The following equations (11) to (14) can be obtained by substituting theequations (9) and (10) for the equations (3) to (5), from which it isunderstood that the force R in the radial direction of the tire and theforce T in the peripheral direction of the tire can be determined fromthe changes ΔHθ_(φ1) and ΔHθ_(φ2) of the peripheral component of themagnetic flux density obtained on two different directions φ1 and φ2,while the force R in the radial direction of the tire can be determinedfrom the change ΔHr_(φ3) of the radial component of the magnetic fluxdensity obtained on a given direction φ3.R=(N1(φ2)·ΔHθ _(φ1) −N1(φ1)·ΔHθ _(φ2))/NN   (11)T=(M1(φ1)·ΔHθ _(φ2) −M1(φ2)·ΔHθ _(φ1))/NN   (12)R=ΔHr _(φ3)/(B2·M 2(φ3))  (13)provided that NN=A1·MM  (14)

The above is described with respect to the generalized principle of themethod for measuring the force R in the radial direction and/or theforce T in the peripheral direction acting upon the tire 1 from thechange of the magnetic flux density in the peripheral direction or theradial direction detected by the magnetic sensor 8A or 8B. Instead ofφ1, φ2 and φ3 used as the above specified direction φ can be useddirection φmax corresponding to a maximum value of a peripheral changeof the magnetic density, direction φmin corresponding to a minimum valueof the peripheral change of the magnetic density and direction φmax1corresponding to a maximum value of a radial change of the magneticdensity, respectively. For example, φmax and φmin change in accordancewith the acting forces R and T and are not constant values, but if theforces R and T are decided, values of magnetic density componentsΔHθ_(φmax) and ΔHθ_(φmin) corresponding to these directions areprimarily defined, and hence R and T can be calculated back from thevalues of ΔHθ_(φmax) and ΔHθ_(φmin). In this case, even when thedirections φmax, φmin and φmax1 are not specified by the measurement,ΔHθ_(φmax), ΔHθ_(φmin) and ΔHr_(φmax1) can be specified by holdingvalues of peaks as a peak value of the change of each component of themagnetic flux density, and the measurement of the direction can be madeuseless.

When the specified values are set instead of φ1 to φ3 as mentionedabove, as seen from FIG. 2 a, if the force T in the peripheral directionof the tire is zero, the peripheral component Dθ of the displacement Dforms a displacement distribution symmetrical with respect to a groundcontact center in the peripheral direction of the tire to establish thefollowing equation (15), and also if the force T in the peripheraldirection is acted, the peripheral component Dθ of the displacement D indirections φmax and φmin symmetrical with respect to the ground contactcenter in the peripheral direction of the tire is rendered into a sum ofadding a displacement in the peripheral direction of the tire of thesame amount in the same direction to establish the following equation(16).M1(φmax)=−M1(φmin)  (15)N1(φmax)=N1(φmin)  (16)

Also, the following equations (17) and (18) can be obtained bysubstituting the equations (15) and (16) for the equations (11) and(12).R=(ΔHθ _(φmax) −ΔHθ _(φmin))/AA  (17)T=(ΔHθ _(φmax) +ΔHθ _(φmin))/AA  (18)R=ΔHr _(φmax1)/(B 2·M 2(φmax1))  (19)provided that AA=2·A1·M1(φmax)·N1(φmax)  (20)

Although the above is described with respect to the principle of themethod for determining the force R in the radial direction of the tireand the force T in the peripheral direction of the tire acting to thetire from changes of magnetic flux densities detected by the magneticsensors 8A, 8B fixed to the rim 6 when the tire 1 is rotated once, asystem for obtaining friction coefficient on road surface used in ABSfrom time changes of magnetic flux densities actually detected by themagnetic sensors 8A, 8B is described with reference to FIGS. 8-9.

FIG. 8 is a system construction view illustrating a construction exampleof a force measuring system 19 in which a force is measured by themethod for measuring forces acted upon the tire according to the aboveembodiments and the measured value of the force is output onto ABS inreal time. The force measuring system 19 comprises a transmitting device7 disposed on a rim 6 of each wheel in a vehicle 5 and a receivingdevice 12 disposed on a vehicle body side of the vehicle 5. Thetransmitting device 7 comprises a transmission side CPU 9 for readingvalues of magnetic flux densities detected by a pair of magnetic sensors8 in a given sampling time and calculating maximum value and minimumvalue of the change of these magnetic flux densities, and a transmissionantenna 11 for receiving the calculated maximum value and minimum valuefrom the transmission side CPU 9 and transmitting them to the receivingdevice 12. Also, the receiving device 12 comprises a receiving antenna13 for receiving signals from the transmission antenna 11, and areceiving side CPU 14 for calculating forces acted upon the tireaccording to the above principle based on the maximum value and minimumvalue of the change of the magnetic flux densities and outputting thecalculated results to ABS 18.

A method for determining maximum value and minimum value from changes ofmagnetic flux densities of respective components detected by the pair ofthe magnetic sensors 8 is as follows. FIG. 9 a shows a time change ΔHθof a peripheral component of the magnetic flux density detected by themagnetic sensor 8A during the running of the vehicle, and FIG. 9 b showsa change ΔHr of a radial component of the magnetic flux density detectedby the magnetic sensor 8B. When the magnetic sensor 8 locates at aposition separated apart from the ground contact face, ΔHθ is zero.While, when the magnetic sensor 8 passes through the ground contact faceor through a zone in the vicinity thereof, as seen from FIGS. 6-7, theperipheral component ΔHθ of the magnetic flux density appears as apattern K. In this pattern K, ΔHθ starts from zero and takes a minimumvalue ΔHθ_(φmin)(1) and then ΔHθ_(φmax)(1) with the lapse of time t.Although the maximum value may appear at two places in the pattern K,the maximum value appearing after the minimum value ΔHθ_(φmin)(1) isonly one place, which is ΔHθ_(φmax)(1). Then, the forces acting to thetire during one rotation of the tire can be determined based on theaforementioned principle from a pair of ΔHθ_(φmin)(2) and ΔHθ_(φmax)(2)and a pair of ΔHθ_(φmin)(3) and ΔHθ_(φmax)(3) successively appearingevery one rotation of the tire.

Moreover, the values of ΔHθ_(φmax) and ΔHθ_(φmin) can be specified asinflection points of maximum and minimum by reading values of ΔHθ at agiven sampling time and comparing the read values with values readimmediately prior to the reading. In the embodiments of the invention,it is important that these maximum value and minimum value can bespecified irrespectively of a vehicle speed. That is, even if the timerequired for the one rotation of the tire is T1 or T2, ΔHθ_(φmax) andΔHθ_(φmin) can be specified without measuring a period of the time, sothat the system can be constructed simply in a high precision withoutmeasuring a rotating speed of a wheel and using the rotating speed ofthe wheel in the calculation treatment of the forces. Similarly, maximumvalues ΔHr_(φmax1)(1), ΔHr_(φmax1)(2) and ΔHr_(φmax1)(3) of the radialcomponent of the magnetic flux densities shown in FIG. 9 b can bedetermined every one rotation of the tire.

In the above case, a pair of the magnet 4 and the magnetic sensor 8arranged on one straight line extending inward and outward in the radialdirection of the tire is one pair on the tire 1, but it may be disposedat two or more places on the periphery within a range not causing aninterference of magnetic force to each other, whereby it is possible toshorten the measuring period and conduct the measurement of forces in ahigher precision.

In the invention, the sheet-shaped magnet 4 attached to the tire 1 ispreferable to have a flexibility provided by mixing and dispersingmagnetic powder of ferrite or a rare earth magnetic body such assamarium-cobalt, iron-neodymium-boron or the like with rubber or aresin. Thus, the magnet 4 can be deformed following to the deformationof the tire, whereby the breakage of the magnet 4 or the peeling fromthe tire 1 can be prevented and also the breakage due to vibrationsthrough the running vehicle or shocks can be prevented.

As the magnetic sensor 8A, 8B, it is preferable to use MI sensor or MRsensor capable of detecting a magnetic flux density of a magnetic fieldeven at a position separated apart from the magnet 4 in a goodsensitivity. Moreover, the force R in the radial direction of the tireand the force T in the peripheral direction of the tire can besimultaneously measured by only the 8A detecting the peripheralcomponent among the magnetic sensors 8A and 8B, so that the magneticsensor 8B used for detecting only the force R in the radial direction ofthe tire may be omitted, but it can be applied for checking the resultsmeasured by the magnetic sensor 8A by using together with the magneticsensor 8A.

Then, a second embodiment of the invention is described with referenceto FIGS. 10-14. In these figures, the same parts as in the firstembodiment are represented by the same numerals. FIG. 10 is a sectionview of the tire 1 at a meridional plane of the tire, and FIG. 11 is aperspective view showing an arrangement of sheet-shaped magnets 24A,24B. To inner surface of a tread portion 2 of the tire 1 in a radialdirection of the tire are attached two sheet-shaped magnets 24A, 24Bhaving a flexibility and the same characteristics. These magnets 24A,24B have magnetic poles having opposite polarities at both ends thereofand are arranged side by side in a peripheral direction of the tire sothat the magnetic poles of these magnets are opposite to each other in awidthwise direction of the tire. That is, if N-pole of the magnet 24Alocates at left side in the widthwise direction of the tire, N-pole ofthe magnet 24B locates at right side in the widthwise direction of thetire. These magnets 24A, 24B cooperate with each other to form a magnet24 forming a magnetic field to be detected. Therefore, the magnet 24 isattached so as to coincide the center thereof with a point P on an innerperipheral face of the tire.

On the other hand, a transmitting device 7 is attached to an outersurface of a rim well portion 6A of a rim 6 in the radial direction ofthe tire and a magnetic sensor 28 is fixed thereinto at a posture ofdetecting a magnetic flux density Hz in the widthwise direction of thetire. Under no action of external force to the tire, the magnetic sensor28 locates on a straight line L1 passing through the point P andextending inward and outward in the radial direction of the tire and isarranged on an equatorial plane E located at a center in the widthwisedirection of the tire. The magnet 24 and the magnetic sensor 28constitute an apparatus 20 for measuring forces acted upon the tire.

FIG. 12 is a schematically developed view showing widthwise component Fof a magnetic flux density by arrows in a magnetic field formed by themagnet 24 comprised of the magnets 24A, 24B on a peripheral face havingthe same height in the radial direction of the tire as in the magneticsensor 28. In this figure, a point M shows a position of detecting themagnetic field by the magnetic sensor 28. When the displacement D of thepoint P on the tread portion 2 attached with the magnet 24 is zero, i.e.the action of external force to the tire is none, the center P of themagnet 24 coincides with M. Moreover, symbol C shows a peripheraldirection of the tire and symbol W shows the widthwise direction of thetire.

In FIG. 12, when a magnitude of the widthwise component F of themagnetic flux density is shown by a length of the arrow and a directionof F is shown by a direction of the arrow directing from N-pole toS-pole, the widthwise component of the magnetic flux density isleft-directing at an inside of the magnet 24A in the radial directionand right-directing at an inside of the magnet 24B in the radialdirection, and these directions are reversed in the vicinity of a middlebetween the magnets 24A and 24B in the peripheral direction. When thedisplacement of the point on the tread portion 2 attached with themagnet is zero, the widthwise component Hz of the magnetic force linesat the detecting position M of the magnetic sensor 28 is zero.

When the displacement Dθ in the peripheral direction of the tire iscaused at the point P, the magnetic field formed by the magnet 24 andthe position M of the magnetic sensor are relatively shifted to eachother in the peripheral direction. That is, the point M relatively movesto the widthwise component F of the magnetic flux density in a directionperpendicular thereto in FIG. 12, so that the widthwise component Hz ofthe magnetic flux density detected by the magnetic sensor 28 becomes notzero. Within a range of a usually creatable displacement, a displacementamount Dθ in the peripheral direction and a change ΔHz of the widthwisecomponent Hz of the magnetic flux density to a value when Dθ is zero aresubstantially proportional to each other and the following equation (21)is established. In this case, A3 is a proportional constant and Hz iszero when the displacement is zero, so that ΔHz itself shows Hz.ΔHz=A3·Dθ  (21)

As seen from the case of the first embodiment with reference to FIGS. 2and 3, a graph showing a dependency of ΔHz upon the force R in theradial direction and the force T in the peripheral direction is shown inFIG. 13. FIG. 13 a is a graph showing a dependency of the change ΔHz ofthe peripheral component of the magnetic flux density upon the force Rin the radial direction (T=0), and FIG. 13 b is a graph showing adependency of ΔHz to the force T in the peripheral direction (R=R0).

The force R in the radial direction and the force T in the peripheraldirection can be determined from the detected Hz by substituting twovalues of the detected ΔHz, i.e. maximum value ΔHz_(φmax) and ΔHz_(φmin)for equations (22)-(24) derived in the same manner as in the equations(17), (18), (20) used in the explanation of the first embodiment.R=(ΔHz _(φmax) −ΔHz _(φmin))/AA  (22)T=(ΔHz _(φmax) +ΔHz _(φmin))/AA  (23)provided that AA=2·A3·M1(φmax)·N1(φmax)  (24).

Moreover, M1(φmax) and N1(φmax) are values determined by the equation(1) in a direction φmax giving a maximum value ΔHz_(φmax).

The construction of the force measuring system in which forces areactually measured based on the method for measuring forces acted uponthe tire in the second embodiment and then the measured values of theforces are output to ABS in a real time, and the method for determiningmaximum value ΔHz_(φmax) and minimum value ΔHz_(φmin) from the change ΔHof the magnetic flux density on the widthwise component detected by themagnetic sensor 28 are the same as in the first embodiment and thedetailed explanation thereof is omitted here.

The time change of the magnetic flux densities detected is shown in agraph plotting a time on an abscissa. In general, an influence of earthmagnetism is actually developed in results of the above magneticmeasurement, so that if this influence is large, it is required toeliminate the influence. Although a direction of the earth magnetism isconstant irrespectively of the rotation of the tire, since the magneticsensor 8, 28 rotates together with the rotation of the tire 1, when thedirection of magnetism to be measured is a direction other than thewidthwise direction of the tire as in the first embodiment, a waveformof a linear harmony function through the earth magnetism appears.Therefore, the waveform measured by the magnetic sensor 8 in the firstembodiment is formed by overlapping the waveform shown in FIG. 9 throughthe magnetic field formed by the magnet 4 with the waveform of thelinear harmony function through the earth magnetism, so that the maximumvalue and minimum value through the earth magnetism appear in additionto the maximum value and minimum value of the magnetic field through themagnet 4, and hence if the influence of the earth magnetism is large,there is caused a problem on the identification of the maximum value andminimum value.

In the measuring method of the second embodiment, however, the magneticflux density in the widthwise direction of the tire, i.e. the magneticflux density in the direction parallel to the rotating axis of the tireis measured, so that the direction measured to the road surface isunchangeable even when the magnetic sensor 28 arrives at any positionaccompanied with the rotation of the tire, and hence the earth magnetismbecomes constant irrespectively of the rotation of the tire and theinfluence of the earth magnetism is not revealed in the rotation of thetire. Therefore, the identification of the maximum value and minimumvalue of the widthwise component of the magnetic field of the magnet 24as it is expected can be carried out by the aforementioned method.

Moreover, the method of the latter embodiment can remove the change ofthe influence of the earth magnetism accompanied with the rotatingposition of the tire, but can not eliminate the influence of the earthmagnetism changing by the direction of the vehicle or a vehicle runningarea. If it is required to remove the latter influence, forces acting tothe tire not influenced by the earth magnetism can be determined bydetecting the position or direction of the vehicle to determine earthmagnetism and subtracting the influenced amount from the measured valueof the magnetic flux density to conduct the correction thereof.

The formation example of the sheet-shaped magnets 24A, 24B and magneticsensor 28 used in the second embodiment is the same as in the firstembodiment and the detailed explanation thereof is omitted here.

Then, a third embodiment is described with reference to FIGS. 15-17. Inthese figures, the same parts as in the first embodiment are shown bythe same numerals. FIG. 15 is a section view of the tire 1 at ameridional plane of the tire, and FIG. 16 is a section viewcorresponding to an arrow A2-A2 of FIG. 15. In the tread portion 2 ofthe tire 1 is arranged a steel belt 3 comprised of two belt layerscontaining steel cords, and one rectangular sheet-shaped magnet 34 isattached to an inner face of the tread portion 2 in the radial directionof the tire or an inner peripheral face 2 a of the tire at a point P ofa widthwise center so as to coincide the center with the point P, whilea magnetic sensor 38 is fixed onto an outer surface of a rim wellportion 6A of a rim 6 in the radial direction of the tire at a widthwisecenter thereof. The magnet 34 is arranged so as to extend one side ofthe rectangle in the peripheral direction of the tire, and the magneticsensor 38 is arranged so as to position its magnetic detecting center ona straight line L passing through the point P and extending inward andoutward in the radial direction of the tire, and an apparatus 30 formeasuring forces acted upon the tire is constituted with thesheet-shaped magnet 34 and the magnetic sensor 38.

The magnetic sensor 38 is comprised of a sensor 38A detecting a radialcomponent Hr and a sensor 38 b detecting a peripheral component Hθ in amagnetic field formed by the magnet 34. To the rim 6 is attached atransmitting device 7 for treating signals input from the magneticsensor 38 through a junction line and a connector (not shown) andtransmitting to a receiving device disposed on a vehicle body.

The magnet 34 is constructed so that the polarity differs between frontand back. For example, N-pole 34 n is formed on an inner face of themagnet 34 in the radial direction of the tire or a non-adhesion face andS-pole 34S is formed on an outer face in the radial direction of thetire or an adhesion face. Also, the magnet 34 is formed at a uniformthickness, and magnetization of N-pole or S-pole is uniformlydistributed over a whole of each respective face.

FIG. 17 a is a schematic view showing a distribution of magnetic forcelines radiated from the sheet-shaped magnet 34 attached to the innerperipheral face 2 a of the tread portion 2. If the steel belt 3 is notexistent, the form of the magnetic force lines of the magnet 34 havingthe magnetization uniformly distributed over the whole of the face is aplane symmetry with respect to a magnet plane as a symmetrical plane asshown by dotted lines in the figure. However, the steel belt 3 isactually arranged just near to the inner peripheral face 2 a attachedwith the magnet 34, so that the magnetic force lines passing through theinterior of the tread portion 2 pass through the steel cords having ahigh permeability and hence the magnetic force lines form thedistribution similar to that when S-pole is formed in a region aroundthe magnet 34 in the inner peripheral face 2 a of the tire. Further, anintensity of the magnetic field is equal to or more than that in case ofusing no steel belt 3, for example, at a point just above a center ofN-pole face.

Even in the magnet 4 used in the first embodiment, the similardistribution of the magnetic force lines is formed, and a detail of sucha magnetic force line distribution is shown in FIG. 17 b in the formcompared with FIG. 17 a. When the magnet 4 is attached to the innerperipheral face 2 a of the tread portion 2 having no steel belt 3, themagnetic force line distribution symmetrical between the front and theback is formed as shown by dotted lines in FIG. 17 b, while when thetread portion 2 has the steel belt 3, almost all of the magnetic forcelines pass through the steel cords to reduce magnetic force linesdistributed on an outside of the tire 1.

If the magnet 4 is made large, the magnetic field enough to be detectedby the magnetic sensor 8 can be formed, but there is a possibility thatunnecessary unbalance is given to the tire and hence performancesinherent to the tire such as ride comfort and the like are damaged. Onthe contrary, in the magnet 34 having different polarities at front andback faces used in the third embodiment, the magnetic force linespassing through the steel cords are necessarily distributed even at theoutside of the tire 1, so that the magnetic field at the detectingposition of the magnetic sensor 38 is not reduced due to the presence ofthe steel cords, and the given object can be attained by a lightermagnet, which is more advantageous as compared with the magnet 4 of thefirst embodiment in a point that the tire performances such as ridecomfort and the like are not badly affected.

Insofar as the magnet 34 being advantageous as compared with the magnet4 of the first embodiment is used in the tire having the steel cords asmentioned above, the radiated form of the magnetic force lines is thesame as shown in the first embodiment and the force in the peripheraldirection acting to the tire and the force in the radial directionacting to the tire can be measured in the same manner as described inthe first embodiment, so that the detailed explanation thereof isomitted here.

Next, a fourth embodiment is described with reference to FIGS. 18-21.FIG. 18 is a section view at a meridional plane of the tire, and FIG. 19is a perspective view showing an arrangement of a magnet 44. In thetread portion 2 of the tire 1 is arranged the steel belt 3 comprised oftwo belt layers having steel cords therein, and the magnet 44 comprisedof four sheet-shaped magnets 44 a, 44 b, 44 c and 44 d is attached to aninner face of the tread portion 2 of the tire 1 in the radial directionof the tire, and a magnetic sensor 48 is attached to a rim well portion6A of a rim 6 opposing to the magnet 44, and hence an apparatus 40 formeasuring forces acted upon the tire is constituted with the magnet 44and the magnetic sensor 48.

The magnetic sensor is attached to a rim well portion 6A in a positionon an equatorial plane E of the tire at a posture of detecting amagnetic flux density Hz in the widthwise direction, and also to the rim6 is attached a transmitting device 7 for treating signals input fromthe magnetic sensor 48 through a junction line and a connector (notshown) and transmitting to a receiving device disposed on a vehiclebody.

Each of the sheet-shaped magnets 44 a, 44 b, 44 c and 44 d is made of arubber sheet being rectangular at the same size and having anapproximately uniform thickness over the full face, in which themagnetization is approximately uniformly distributed on each face. Also,they are arranged so that a center of each rectangle is positioned ineach apex of a rectangle R centering a point P on the inner peripheralface of the tire and directing one side in the peripheral direction andeither side of each of them is directed in parallel to the peripheraldirection of the tire. Further, the magnetic sensor 48 is arranged sothat a magnetic detecting center is positioned on a straight line L2passing through the point P and extending inward and outward in theradial direction of the tire.

Furthermore, the polarities in the inner faces of the magnets in theradial direction located at mutually adjoining apexes of the rectangle Ror the non-adhesion faces are opposite to each other. In the embodimentof FIG. 19, the polarities of the magnets 44 a, 44 d located at opposingcorners and inside in the radial direction are magnetized to N-pole, andthe polarities of the magnets 44 b, 44 c located at different opposingcorners and inside in the radial direction are magnetized to S-pole.

FIG. 20 is a schematic view showing a distribution of magnetic forcelines from the magnet 44 having the above construction, in which FIG. 20a shows a distribution of magnetic force lines at a sectioncorresponding to an arrow a-a of FIG. 19, and FIG. 20 b shows adistribution of magnetic force lines at a section corresponding to anarrow b-b of FIG. 19. The magnetic force lines radiated between themagnets 44 a and 44 b lining in the widthwise direction of the tire andthe magnetic force lines radiated between the magnets 44 c and 44 dlining in the widthwise direction of the tire are opposite to each otherin the widthwise direction of the tire, while they are distributed atthe outside of the tire without being influenced by the steel belt 3.

FIG. 21 is a schematically developed view showing a widthwise componentF of the magnetic flux density in the magnetic field formed by themagnet 44 on an equator E having the same height in the radial directionof the tire as in the magnetic sensor 48 viewing from a side of arotating center of the tire. In this figure, a point M shows a magneticdetecting position of the magnetic sensor 48. When the displacement D ofthe point P is zero, the center of the magnet 44 coincides with M inFIG. 21. Moreover, an arrow C shows a peripheral direction of the tireand an arrow W shows a widthwise direction of the tire.

In FIG. 21, when a magnitude of the widthwise component F of themagnetic flux density is a length of the arrow and a direction of Fshows a direction of the arrow indicating a direction from N-pole toS-pole, the arrow of F is left-directing at the inside between themagnets 44 a and 44 b in the radial direction, while it isright-directing at the inside between the magnets 44 c and 44 d in theradial direction, and also the direction of the magnetic force lines isreversed at a middle position of the magnet 44 in the peripheraldirection. That is, when the displacement D of the point P is zero, thewidthwise component Hz of the magnetic flux density is zero at thedetecting position M of the magnetic sensor 48.

The form of the magnetic force lines shown in FIG. 21 is quite the sameas described in the second embodiment, and hence the force in theperipheral direction and the force in the radial direction acting to thetire can be measured in the same manner as described in the secondembodiment, so that the detailed explanation is omitted here. Moreover,this embodiment is different from the second embodiment in a point thatwhen the steel belt 3 is disposed in the tire, the stronger magneticfield can be formed by this embodiment, which is as explained on thecomparison between the first embodiment and the third embodiment.

Next, a modified example of the fourth embodiment is described withreference to FIGS. 22-25 using a magnet 54 instead of the magnet 44.FIG. 22 is a section view of the tire 1 at a meridional plane of thetire, and FIG. 23 is a perspective view showing an arrangement of themagnet 54. To the inner face of the tread portion 2 of the tire 1 in theradial direction is attached the magnet 54 comprised of two sheet-shapedmagnets 54 a, 54 b, and a magnetic sensor 58 is attached to a rim wellportion 6A of a rim 6 facing to the magnet 54, and an apparatus 50 formeasuring forces acted upon the tire is constructed with the magnet 54and the magnetic sensor 58.

The magnetic sensor 58 is attached to the rim well portion 6A in aposition on an equatorial plane E of the tire at a posture of detectinga magnetic flux density Hz in the widthwise direction likewise thefourth embodiment, and also to the rim 6 is attached a transmittingdevice 7 for treating signals input from the magnetic sensor 58 througha junction line and a connector (not shown) and transmitting to areceiving device disposed on a vehicle body.

Each of the sheet-shaped magnets 54 a and 54 b is made of a rubber sheetbeing rectangular at the same size and having an approximately uniformthickness over the full face, in which the magnetization isapproximately uniformly distributed on each face. These magnets 54 a, 54b are arranged so that centers thereof are positioned in a pair ofapexes of a rectangle R centering a point P on the inner peripheral faceof the tire and directing in the peripheral direction and either side ofeach of them is directed in parallel to the peripheral direction of thetire. Further, the magnetic sensor 58 is arranged on a straight line L3passing through the point P and extending in the radial direction of thetire under no action of external force to the tire.

The polarities of magnetic poles in these magnets 54 a, 54 b at an innerface in the radial direction or a non-adhesion face thereof are thesame. In the example of FIG. 23, the polarities of the magnets 54 a, 54b at the inside in the radial direction are magnetized to S-pole.

FIG. 24 is a schematic view showing a distribution of magnetic forcelines from the magnet 54 having the above construction, in which FIG. 24a shows a distribution of magnetic force lines at a sectioncorresponding to an arrow a-a of FIG. 23, and FIG. 24 b shows adistribution of magnetic force lines at a section corresponding to anarrow b-b of FIG. 23. Also, FIG. 25 is a schematically developed viewshowing a widthwise component F of the magnetic flux density in themagnetic field formed by the magnet 44 on an equator E having the sameheight in the radial direction of the tire as in the magnetic sensor 58viewing from a side of a rotating center of the tire.

The magnetic poles of the magnets 54 a, 54 b at an outer face in theradial direction of the tire or an adhesion face are N-poles in FIG. 23.The magnetic force lines directing from these N-poles to S-poles of themagnets 54 a, 54 b at an outer face in the radial direction of the tireor a non-adhesion face are distributed so as to pass through the steelbelt 3 and intersect the inner peripheral face 2 a at opposite positionsof the magnets 54 a, 54 b in the widthwise direction of the tire withrespect to the equatorial plane E and direct toward the respectiveS-poles. When the magnetic force line distribution shown in FIG. 25 iscompared with the aforementioned magnetic force line distribution shownin FIG. 20, it is clear that they are substantially the samedistribution, which means that the magnet 54 comprised of two magnets 54a and 54 b also forms the same magnetic field as the magnet 44 comprisedof four magnets 44 a, 44 b, 44 c and 44 d.

In FIG. 25, C is a peripheral direction of the tire and W is a widthwisedirection of the tire. When the displacement D of the point P is zero,the center of the magnet 54 coincides with a magnetic detecting positionM of the magnetic sensor 58. In this figure, when a magnitude of thewidthwise component F of the magnetic flux density is a length of thearrow and a direction of F shows a direction of the arrow indicating adirection from N-pole to S-pole, the arrow is left-directing on anequator E in the peripheral position corresponding to the magnet 54 a,while the arrow is right-directing on the equator E in the peripheralposition corresponding to the magnet 54 b, and the direction of thearrow is reversed at a middle position of the magnet 54 in theperipheral direction. That is, the modified example also means that theforce-T in the peripheral direction of the tire and the force R in theradial direction of the tire can be measured in the same manner asdescribed in the second embodiment, so that the detailed explanation onthis modified example is omitted.

Then, a fifth embodiment of the invention is described with reference toFIGS. 26-30. FIG. 26 is a section view of the tire 1 at a meridionalplane thereof, and FIG. 27 is a perspective view showing an arrangementof a magnet and a magnetic sensor. In the tread portion 2 of the tire 1is arranged the steel belt 3 comprised of two belt layers having steelcords therein, and six sheet-shaped magnets 64 a, 64 b, 64 c, 64 d, 64 eand 64 f are attached to an inner face of the tread portion 2 of thetire 1 in the radial direction of the tire, and two magnetic sensors68A, 68B are attached to a rim well portion 6A of a rim 6 at a postureof detecting widthwise components of respective magnetic flux densities.

Each of the six sheet-shaped magnets 64 a, 64 b, 64 c, 64 d, 64 e and 64f is made of a rubber sheet being rectangular at the same size andhaving an approximately uniform thickness over the full face, in whichthe magnetization is approximately uniformly distributed on each face soas to make polarities of front and back faces different. Also, thesemagnets 64 a, 64 b, 64 c, 64 d, 64 e and 64 f are arranged in three rowssymmetrical with respect to an equatorial plane E and every two alongthe peripheral direction at equal intervals, in which a side of each ofthese magnets is directed in parallel to the peripheral direction anddistances separated between the adjoining magnets in the peripheraldirection and in the widthwise direction are not more than 100 mm,respectively, and directions of magnetic poles are opposite to eachother between the adjoining magnets in the peripheral direction and thewidthwise direction of the tire. For example, the three sheet-shapedmagnets 64 b, 64 d and 64 f adjoining the sheet-shaped magnet 64 ehaving N-pole at an outside in the radial direction are arranged so asto have N-pole at an inside in the radial direction different from 64 e.

These six sheet-shaped magnets 64 a, 64 b, 64 c, 64 d, 64 e and 64 f canbe seen to constitute a double magnet of a first magnet 64A consistingof the four sheet-shaped magnets 64 a, 64 b, 64 e and 64 d arranged atapexes of a first rectangle R_(A), respectively, and a second magnet 64Bconsisting of the four sheet-shaped magnets 64 b, 64 c, 64 f and 64 earranged at apexes of a second rectangle R_(B), respectively. Under noaction of external force to the tire 1, a first magnetic sensor 68A isarranged at a point Q_(A) of the rim on a straight line passing througha center P_(A) of the rectangle R_(A) in the radial direction, and asecond magnetic sensor 68B is arranged at a point Q_(B) of the rim on astraight line passing through a center P_(B) of the rectangle R_(B) inthe radial direction. As a result, an apparatus 60 for measuring forcesacted upon the tire is constituted with the first and second magnets64A, 64B consisting of the six sheet-shaped magnets 64 a, 64 b, 64 c, 64d, 64 e and 64 f and the first and second magnetic sensors 68A, 68B.

The apparatus 40 for measuring forces acted upon the tire according tothe fourth embodiment can remove the influence of the change of earthmagnetism on the rotating position of the tire, but can not remove theinfluence of earth magnetism changing in accordance with the position ordirection of the vehicle unless another means for measuring the earthmagnetism is used together. On the contrary, the apparatus 60 formeasuring forces acted upon the tire according to the fifth embodimentis not subjected to the influence even if the earth magnetism changes inaccordance with the position or direction of the vehicle and isadvantageous in a point that the influence of earth magnetism is notcorrected separately. Next, the action of the latter apparatus isexplained.

FIG. 28 is a schematic view showing a distribution of magnetic forcelines from the magnets 64A, 64B having the above construction, in whichFIG. 28 a shows magnetic force lines at a section corresponding to anarrow a-a of FIG. 27, and FIG. 28 b shows magnetic force lines at asection corresponding to an arrow b-b. The magnetic force lines radiatedamong the magnets 64 a, 64 b, 64 c arranged side by side in thewidthwise direction of the tire and the magnetic force lines radiatedamong the magnets 64 d, 64 e, 64 f are the same form, but they areformed so as to make directions of these magnetic force lines at thedifferent sections opposite to each other.

FIG. 29 is a schematically developed view showing a widthwise componentF of the magnetic flux density in the magnetic field formed by themagnets 64A, 64B on an equator E having the same height in the radialdirection of the tire as in the magnetic sensors 68A, 68B viewing from aside of a rotating center of the tire. In this figure, a point Q_(A) isa magnetic detecting position of the magnetic sensor 68A, and a pointQ_(B) is a magnetic detecting position of the magnetic sensor 68B, andan arrow C is a peripheral direction of the tire and an arrow W is awidthwise direction of the tire.

In FIG. 29, when the magnitude of the widthwise component F of themagnetic flux density is shown by a length of an arrow and an arrow fromN-pole to S-pole is left-directing as a plus direction, the widthwisecomponent F of the magnetic flux density in the magnetic field formed bythe magnet 64A in the vicinity of the point Q_(A) decreases toward theperipheral direction C and reverses at the point Q_(A) from plus tominus, while the widthwise component F of the magnetic flux density inthe magnetic field formed by the magnet 64B in the vicinity of the pointQ_(B) increases toward the peripheral direction C and reverses at thepoint Q_(B) from minus to plus. In other words, the magnets 64A and 64Bare arranged so as to come close to each other and render the change ofthe widthwise component F of the magnetic flux density along theperipheral direction C of the tire under no action of external force tothe tire into a reversal relation.

As seen from FIG. 29, the change of the widthwise component of themagnetic flux density in the peripheral direction in the vicinity of thepoints Q_(A), Q_(B) is the same as in FIG. 12 corresponding to thesecond embodiment or a reversal thereof, so that the forces R and T canbe determined based on the equations (22)-(24) as explained in thesecond embodiment. However, since the change of the earth magnetism dueto the direction or position of the vehicle is ignored in the method ofthe second embodiment as previously mentioned, a sum of widthwisecomponent F_(G) through the earth magnetism and widthwise component Fthrough the magnet 64A, 64B is actually detected by the magnetic sensor68A, 68B, so that the forces R and T determined by the equations(22)-(24) based on such sum of widthwise components are subjected to aninfluence of changing F_(G) and become low in the precision.

The method of the fifth embodiment intends to completely remove theinfluence of the earth magnetism by taking out only the change ofmagnetic flux density F through the magnet from the change of magneticflux density detected and applying the equations (22)-(24) thereto. Amethod of extracting F is described below. FIG. 30 is a graph showing achange ΔHz of widthwise magnetic flux density when the tire 1 is rotatedin the direction C by using a direction φ on an abscissa, in which FIG.30 a shows ΔHz detected by the magnetic sensor 68A, and FIG. 30 b showsΔHz detected by the magnetic sensor 68B, and FIG. 30 c is a reversal ofthe graph of FIG. 30 b.

In these figures, a curve PTa of magnetic flux density change actuallydetected is a total of a curve PTa0 of magnetic flux density changethrough only the magnet 64A and earth magnetism F_(G), and similarly PTbis a total of a curve PTb0 of magnetic flux density change through onlythe magnet 64B and earth magnetism F_(G). In this case, the changes ofthe magnetic fields formed by the magnets 64A, 64B in the peripheraldirection have a reversal relation, so that PTa0 and PTb0 are curvesreversing to each other with respect to an axis of ΔHz=0, and F_(G) actsin the same direction in any cases. Now, the curve PTb of FIG. 30 b isreversed to obtain a curve PTc as shown in FIG. 30 c and then the curvesPTa and PTc are arithmetically added to obtain a curve PTd as shown inFIG. 30 d, whereby the component through the earth magnetism can berendered into zero to extract only the components through the magnets64A and 64B.

As seen from the above, the forces R and T can be determined byreplacing ΔHz_(φmax) and ΔHz_(φ) _(min) of the equations (22) and (23)with the following equations (25) and (26) without considering theinfluence of the earth magnetism.ΔHz _(φmax)=(ΔHZ _(φmax-a) +ΔHz _(φmax-c))/2  (25)ΔHz _(φmin)=(ΔHz _(φmin-a) +ΔHz _(φmin-c))/2  (26)

In this case, ΔHz_(φmax-a) and Δ_(Hz) _(φmax-c) are maximum value andminimum value of widthwise magnetic flux density detected by the firstmagnetic sensor 68A, and ΔHz_(φmin-a) and ΔHz_(φmin-c) are maximum valueand minimum value of a curve obtained by reversing the curve ofwidthwise magnetic flux density change detected by the second magneticsensor 68B.

In the above embodiments, the magnet is attached to the inner peripheralface of the tire and the magnetic sensor is attached to the rim. In theinvention, it is enough to measure the relative displacement between thetire tread portion and the rim. Therefore, the similar effects can beobtained by attaching the magnetic sensor to the inner peripheral faceof the tire and the magnet to the rim even in any one of the aboveembodiments. As a modified example of the first embodiment, the casethat the magnet is attached to the rim and the magnetic sensor isattached to the inner peripheral face of the tire is shown in FIGS. 31and 32.

FIG. 31 is a section view of the tire 1 at a meridional plane of thetire, and FIG. 32 is a section view corresponding to an arrow A3-A3 ofFIG. 31. To an inner face in the radial direction and a center in thewidthwise direction of the tread portion 2 of the tire 1 is attached amagnetic sensor 108, while onto an outer face in the radial directionand a center in the widthwise direction of the rim well portion 6A ofthe rim 6 is arranged a magnet 104 having a magnetic pole of onepolarity at its center such as N-pole and magnetic poles of the otherpolarity at both ends such as S-poles so as to position the center on astraight line L4 passing through the magnetic sensor 108 and extendinginward and outward in the radial direction under no action of externalforce to the tire and oppose both ends in the peripheral direction ofthe tire. The magnetic sensor 108 comprises a sensor 108A detecting aradial component Hr in the magnetic field radiated from the magnet 104and a sensor 108B detecting a peripheral component Hθ thereof. Onto therim 6 is attached a transmitting device 7 for treating signals inputfrom the magnetic sensor 108 through a junction line 21 and a connector22 and transmitting to a receiving device disposed on a vehicle body.

When the magnetic sensor or the magnet is attached and fixed to the rim,if it is arranged to separate apart from the rim, a distance to themagnet or magnetic sensor attached to the tire becomes short, so that aweak magnetic force or a light magnet can be detected by the magneticsensor having the same sensitivity, which is advantageous in a pointthat an influence of the tire on unbalance can be reduced. As such anexample, an apparatus 110 for measuring forces acted upon the tire, inwhich the magnetic sensor fixed to the rim is positioned to an outsideof the rim in the radial direction, is explained with reference to FIGS.33-36. FIG. 33 is a section view of the tire 1 showing a section in aplane passing through a rotating axis of the tire, and FIG. 34 is apartial section view illustrating an attaching form of a magnetic sensor118, and FIG. 35 is a partial section view illustrating anotherattaching form of a magnetic sensor 118, and FIG. 36 is a section viewcorresponding to an arrow A4-A4 of FIG. 33.

The apparatus 110 for measuring forces acted upon the tire according tothis embodiment comprises a sheet-shaped magnet 114 attached to an innerface of the tread portion 2 of the tire 1 in the radial direction andhaving a flexibility, and a magnetic sensor 118 measuring a magneticfield from the magnet 114. The magnet 114 has a plane symmetry in whichone of magnetic poles, e.g. N-pole is a center of the plane symmetry andmagnetic poles of the other polarity, e.g. S-poles are disposed at bothends, and is arranged so that a symmetrical plane PL coincides with ameridional plane of the tire under no action of external force to thetire 1 and a radiating direction of magnetic force lines from N-pole ata surface of the magnetic pole directs toward a center in the radialdirection of the tire.

On the other hand, the magnetic sensor 118 is disposed so as to separateoutward from the rim well portion 6A of the rim 6 in the radialdirection of the tire and is positioned on the symmetrical plane PL andcomprises a sensor 118A detecting a radial component Hr of the magneticfield radiated from N-pole and a sensor 118B detecting a peripheralcomponent Hθ.

The attaching form of the magnetic sensor 118 is as follows. Themagnetic sensor 118 is mounted onto a transmitting device 7 for treatingsignals detected by the magnetic sensor 118 to transmit to a receivingdevice disposed on a side of a vehicle body. The transmitting device 7is attached to a block 124. The block 124 is disposed so as to bedisplaceable inward and outward in the radial direction along an innerperipheral face of a cylindrical guide 121 attached to an outer face ofthe rim well portion 6A in the radial direction, while the rotationthereof around the radius of the tire is controlled by a key 129. Here,the block 124 and the guide 121 constitute a stay 120 fixing themagnetic sensor 118 to the rim 6.

On the other hand, a nut 123 is attached to the rim well portion 6A, andan adjusting bolt 125 is threadedly attached to the nut 123 so as toreciprocatedly displace in the radial direction through a turningoperation of its operating part 125 a, and a disc-shaped head 125 b isprovided on a top of the adjusting bold 125. The head 125 b is rotatablyengaged with a disc-shaped cavity portion 124 a of a block 124. The nut123 and the adjusting bolt 125 constitute an adjusting means foradjusting a distance of the magnetic sensor 118 separated from the rim6.

In the thus attached magnetic sensor 118, the distance of the magneticsensor 118 separated from the rim 6 can be adjusted by turning theadjusting bolt 125 to displace the block 124 engaged with thedisc-shaped head 125 b located at the top thereof inward and outward inthe radial direction. Further, the rotation of the block 124 around theradius is controlled, so that the separating distance of the sensor 118can be adjusted without changing the attaching posture of the sensor118. In this way, a fine-tuning of a sensitivity of the magnetic sensor118 can be easily conducted by operating the operating portion 125 a tochange only the separating distance of the magnetic sensor 118 even at astate of mounting the tire 1 onto the rim 6.

On the stay 120 are disposed O-rings 127, 128 for the sealing of a tireinternal pressure, while a fixed nut 126 is also arranged so as to fixthe adjusting bolt 125 after the completion of the fine-tuning toprevent a position shift to vibration shock.

The magnetic sensor 118 may be attached in an attaching form shown inFIG. 35 instead of the attaching form of the magnetic sensor shown inFIG. 34. The transmitting device 7 mounted with the magnetic sensor 118is attached to a block 134. The block 134 is disposed so as to bedisplaceable inward and outward in the radial direction along an innerperipheral face of a cylindrical guide 131 attached to an inner face ofthe rim well portion 6A in the radial direction, while the rotationthereof around the radius of the tire is controlled by a key 139. Here,the block 134 and the guide 131 constitute a stay 130 fixing themagnetic sensor 118 to the rim 6.

To the guide 131 is attached a ring 131 a, and an adjusting bolt 135having collars 135 b, 135 c engaged with the ring 131 a and restrainingan axial displacement through the collars 135 b, 135 c is threadedlyarranged in a female screw hole 134 a formed in the block 134. Theadjusting bolt 135 constitutes an adjusting means for adjusting adistance of the magnetic sensor 118 separated from the rim 6, which canbe reciprocatedly displaced in the radial direction by turning anoperating portion 135 a without rotating the block 134.

Even in the latter attaching form, a fine-tuning of a sensitivity of themagnetic sensor 118 can be easily conducted at a state of mounting thetire 1 onto the rim 6 as previously mentioned. Also, O-rings 137, 138for the sealing of a tire internal pressure are arranged in the stay 130as previously mentioned. In the attaching form shown in FIG. 35, aportion protruding from the rim 6 in the radial direction can be mademinimum, so that the tire 1 is mounted onto the rim 6 at a state ofpositioning the magnetic sensor 118 near to the rim 6 and thereafter themagnetic sensor 118 is separated apart from the rim 6 to approach to themagnet 114, whereby the sensitivity detecting the magnetic field fromthe magnet 114 can be raised and hence the mounting of the tire 1 ontothe rim 6 can be facilitated.

Even in the aforementioned attaching forms, the magnetic sensor 118 isfixed to the rim 6 through the stay 120, 130 at a position separatedapart from the rim 6 in the radial direction of the tire, so that themagnetic sensor 118 is arranged near to the magnet 114 attached to theinner face of the tire, whereby it is possible to detect a change of amagnetic field by the magnetic sensor 118 even in a magnet having a weakmagnetic force and the influence of the magnet 114 on the tire balanceor the like can be made minimum by reducing the weight of the magnet.

In the above explanation, an annular bracket protruding outward from anouter peripheral face of the rim in the radial direction over a fullperiphery can be used instead of the stay 120 protruding outward fromthe outer peripheral face of the rim at one place on the periphery.

Although the above is described with respect to each of the embodiments,the function and effects of the invention are summarized below.Moreover, the following numerals (1)-(19) correspond to the numeralsused in DISCLOSURE OF THE INVENTION.

According to the method for measuring forces acted upon the tire in (1),the forces in the peripheral direction and the radial direction actingto the ground contact face of the tire are determined from a variantpattern of the displacement produced in the ground contact portion ofthe tire, so that these forces can be accurately determined and as aresult, a value of friction coefficient with a high precision can beobtained in real time.

According to the method for measuring forces acted upon the tire in (2),the displacement of the tire portion is measured magnetically, so thatthe influence of noise or the like is less and it is possible to stablyconduct the measurement.

According to the method for measuring forces acted upon the tire in (3),the force acting in the peripheral direction of the tire is determinedfrom an average of maximum value and minimum value in a variant patternof a peripheral component of a magnetic flux density and the forceacting in the radial direction of the tire is determined from adifference between the maximum value and the minimum value, so that themaximum value and minimum value can be specified irrespectively of therotating speed of the tire, and hence it is useless to measure therotating speed of the tire and the measuring system of a high precisioncan be constructed simply.

According to the method for measuring forces acted upon the tire in (4),the force acting in the radial direction of the tire is determined fromthe maximum value or the minimum value in the variant pattern of theradial component of the above magnetic flux density likewise the above,so that it is useless to measure the rotating speed of the tire and themeasuring system of a high precision can be constructed simply.

According to the method for measuring forces acted upon the tire in (5),the force acting in the peripheral direction of the tire is determinedfrom an average of maximum value and minimum value in a variant patternof a widthwise component of the above magnetic flux density and theforce acting in the radial direction of the tire is determined from adifference between the maximum value and the minimum value likewise theabove, so that the maximum value and minimum value can be specifiedirrespectively of the rotating speed of the tire, and hence it isuseless to measure the rotating speed of the tire and the measuringsystem of a high precision can be constructed simply, and further sincethe magnetic sensor measures the magnetic flux density in the widthwisedirection of the tire, the widthwise component of earth magnetism is notchanged accompanied with the rotation of the tire, which does not affectthe identification of the maximum value and minimum value of themagnetic flux density formed by the magnet.

According to the method for measuring forces acted upon the tire in (6),the force acting in the peripheral direction of the tire is determinedfrom an average of maximum value and minimum value in a variant patternof a widthwise component of the above magnetic flux density and theforce acting in the radial direction of the tire is determined from adifference between the maximum value and the minimum value likewise theabove, so that the maximum value and minimum value can be specifiedirrespectively of the rotating speed of the tire, and hence it isuseless to measure the rotating speed of the tire and the measuringsystem of a high precision can be constructed simply, and further it canbe eliminated to change the influence of earth magnetism accompaniedwith the rotation of the tire and also the influence of earth magnetismchanging in accordance with the direction of the vehicle or the runningarea can be eliminated, and hence there can be provided the forcemeasuring method of light weight and high precision.

According to the apparatus for measuring forces acted upon the tire in(7), the magnet is arranged in the inner peripheral face of the treadportion and the magnetic sensor is attached to the outer peripheral faceof the rim, so that the aforementioned force measuring methods can berealized and the measurement of the force and friction coefficientdetermined from the results can be rendered into a high precision.

According to the apparatus for measuring forces acted upon the tire in(8), the magnet is arranged in the outer peripheral face of the rim andthe magnetic sensor is attached to the inner peripheral face of thetread portion, so that the aforementioned force measuring methods can berealized and the measurement of the force and friction coefficientdetermined from the results can be rendered into a high precision.Further, since the magnet is attached to the surface of the rim, therestriction to the weight can be mitigated as compared with the case ofattaching the magnet to the tire, and it is easy to form a strongmagnetic field and it is possible to conduct the measurement of themagnetic field more stably.

According to the apparatus for measuring forces acted upon the tire in(9), the force measuring method of (3) or (4) can be attained by thestructure and arrangement of the magnets.

According to the apparatus for measuring forces acted upon the tire in(10), the force measuring method of (5) can be attained by the structureand arrangement of the magnets.

According to the apparatus for measuring forces acted upon the tire in(11), the magnetizations of polarities are distributed so as to be areverse relation between front and back of the magnet, so that astronger magnetic field can be formed by a synergistic effect with thesteel cords.

According to the apparatus for measuring forces acted upon the tire in(12), the magnetization of the same polarity is uniformly distributed ineach plane of the front and back of a sheet-shaped magnet constitutingthe magnet, so that the magnet capable of forming complicated magneticfields can be simply constituted by arranging the sheet-shaped magnetscut out from a magnetic sheet magnetized to different polarities atfront and back while properly combining them in the front and back.

According to the apparatus for measuring forces acted upon the tire in(13), the force measuring method of (3) or (4) can be attained by thearrangement of the magnet using sheet-shaped magnets of differentpolarities at front and back.

According to the apparatus for measuring forces acted upon the tire in(14), the force measuring method of (5) can be attained by thearrangement of the magnet using sheet-shaped magnets of differentpolarities at front and back.

According to the apparatus for measuring forces acted upon the tire in(15), the force measuring method of (5) can be attained by thearrangement of the magnet using sheet-shaped magnets of differentpolarities at front and back likewise the above, which can be alsoattained by the less number of the sheet-shaped magnets.

According to the apparatus for measuring forces acted upon the tire in(16), the force measuring method of (6) can be attained by thearrangement of the magnets and the arrangement of the magnetic sensors,and hence the forces acting to the tire capable of eliminating not onlythe influence of earth magnetism accompanied with the rotation of thetire but also the influence of earth magnetism changing in accordancewith the direction of the vehicle or the running area can be determinedsimply in a higher precision.

According to the apparatus for measuring forces acted upon the tire in(17), the magnet or magnetic sensor fixed to the rim is arranged at theoutside of the rim in the radial direction, so that the distance betweenthe magnet and the magnetic sensor can be made small, and even if thesize of the magnet is same, the magnetism detected by the magneticsensor can be made strong to improve the measuring precision.

According to the apparatus for measuring forces acted upon the tire in(18), there is provided the stay or annular bracket for fixing themagnetic sensor or magnet to the rim, so that the magnetic sensor ormagnet can be surely fixed to the rim. Also, in case of arranging pluralmagnetic sensors, the annular bracket can be used to more easily attachthese magnetic sensors.

According to the apparatus for measuring forces acted upon the tire in(19), the adjusting means for adjusting the separating distance of themagnetic sensor from the rim is provided and the operating portionactuating the adjusting means is arranged at the inside of the rim inthe radial direction of the tire, so that even after the tire is mountedon the rim, the separating distance of the magnetic sensor from themagnet can be adjusted, and hence the fine adjustment of the sensitivityof the magnetic sensor and the mounting of the tire on the rim can befacilitated.

EXAMPLE

In order to confirm the effectiveness of the invention, an experiment iscarried out using the apparatus 20 for measuring the forces acted uponthe tire according to the second embodiment. The magnetic sensor 28 isattached to a rim of one front wheel in a vehicle, while the magnets24A, 24B are attached to an inside of a tread portion of a tire mountedon this wheel in the radial direction, and the vehicle is run at aconstant speed and braked to add a transitional change to a load balancebetween front and rear wheels of the vehicle and forward and backwardforces thereof, at where (ΔHz_(φmax)−ΔHz_(φmin)) and(ΔHz_(φmax)+ΔHz_(φmin)) shown in the equations (17) and (18) aremeasured based on the method of the second embodiment. In this case, thewheel to be mounted with the tire is a wheel-type sextant force meter,i.e. the wheel itself has a function of a sextant force meter. The forceR acting in the radial direction of the tire and the force T acting inthe peripheral direction of the tire are determined by the wheel-typesextant force meter to examine a correlation therebetween.

In FIG. 37 are plotted found values and calculated values of theseforces measured from a last minute before the braking of the vehicle tothe stop thereof every a given interval, in which FIG. 37 a is acorrelation chart taking the force R acting in the radial directionmeasured by the sextant force meter on an abscissa and Hz-dif shown byan equation (27) on an ordinate, and FIG. 37 b a correlation charttaking the force T acting in the peripheral direction measured by thesextant force meter on an abscissa and Hz-ave shown by an equation (28)on an ordinate.Hz-dif=(ΔHz _(φmax) −ΔHz _(φmin))  (27)Hz-ave=(ΔHz _(φmax) +ΔHz _(φmin))  (28)

A correlation coefficient between Hz-dif and the force R acting in theradial direction of the tire is 0.986, and a correlation coefficientbetween Hz-ave and the force R acting in the peripheral direction of thetire is 0.951. Thus, they show a high correlation, from which it can beconfirmed that the force measuring method according to the invention isvery effective.

INDUSTRIAL APPLICABILITY

As seen from the above, the method for measuring forces acted upon thetire and the apparatus for measuring forces acted upon the tireaccording to the invention can measure force in the radial direction andforce in the peripheral direction acting to the tire required for thehigh precision measurement of a friction force on road surface in ahigher precision simply.

1. A method for measuring at least one of forces in a peripheraldirection and a radial direction of a running tire mounted onto a rimacted upon a ground contact face, in which when a point on an outerperipheral face of the rim is Q and an intersect between a straight linepassing through the point Q under no action of external force andextending in the radial direction and an inner peripheral face of atread portion of the tire is P, said forces are determined from avariant pattern that a relative displacement of the point P to the pointQ in the peripheral direction or the radial direction is changed inaccordance with a rotating position of the point Q when the point Ppasses through the ground contact portion of the tire, wherein amagnetic field formed by a magnet arranged on one of the point P and thepoint Q is continuously measured by a magnetic sensor arranged on theother of the point P and the point Q, and the variant pattern of therelative displacement between the point P and the point Q is determinedby reverse calculation from a variant pattern of a magnetic flux densitychanged in accordance with the relative displacement; and wherein themeasurement of the magnetic flux density is conducted by using themagnet arranged so that a magnetic force line distribution of themagnetic field forms a plane symmetry with respect to a meridional planeof the tire including the point P or the point Q under no action ofexternal force to the tire, and the force acting in the peripheraldirection of the tire is determined from an average between maximumvalue and minimum value of a variant pattern of a tire peripheralcomponent in the measured magnetic flux density and the force acting inthe radial direction of the tire is determined from a difference betweenthe maximum value and the minimum value of the variant pattern.
 2. Amethod for measuring at least one of forces in a peripheral directionand a radial direction of a running tire mounted onto a rim acted upon aground contact face, in which when a point on an outer peripheral faceof the rim is Q and an intersect between a straight line passing throughthe point Q under no action of external force and extending in theradial direction and an inner peripheral face of a tread portion of thetire is P, said forces are determined from a variant pattern that arelative displacement of the point P to the point Q in the peripheraldirection or the radial direction is changed in accordance with arotating position of the point Q when the point P passes through theground contact portion of the tire, wherein a magnetic field formed by amagnet arranged on one of the point P and the point Q is continuouslymeasured by a magnetic sensor arranged on the other of the point P andthe point Q, and the variant pattern of the relative displacementbetween the point P and the point Q is determined by reverse calculationfrom a variant pattern of a magnetic flux density changed in accordancewith the relative displacement; wherein the measurement of the magneticflux density is conducted by using the magnet arranged so that amagnetic force line distribution of the magnetic field forms a planesymmetry with respect to a meridional plane of the tire including thepoint P or the point Q under no action of external force to the tire,and the force acting in the radial direction of the tire is determinedfrom a maximum value or a minimum value of a variant pattern of a tireradial component of the measured magnetic flux density.
 3. A method formeasuring at least one of forces in a peripheral direction and a radialdirection of a running tire mounted onto a rim acted upon a groundcontact face, in which when a point on an outer peripheral face of therim is Q and an intersect between a straight line passing through thepoint Q under no action of external force and extending in the radialdirection and an inner peripheral face of a tread portion of the tire isP, said forces are determined from a variant pattern that a relativedisplacement of the point P to the point Q in the peripheral directionor the radial direction is changed in accordance with a rotatingposition of the point Q when the point P passes through the groundcontact portion of the tire, wherein a magnetic field formed by a magnetarranged on one of the point P and the point Q is continuously measuredby a magnetic sensor arranged on the other of the point P and the pointQ, and the variant pattern of the relative displacement between thepoint P and the point Q is determined by reverse calculation from avariant pattern of a magnetic flux density changed in accordance withthe relative displacement; wherein the measurement of the magnetic fluxdensity is conducted by using the magnet arranged so that a widthwisecomponent of a magnetic flux density of the magnetic field changes alongthe peripheral direction of the tire under no action of external forceto the tire, and the force acting in the peripheral direction of thetire is determined from an average between maximum value and minimumvalue of a variant pattern of a tire widthwise component in the measuredmagnetic flux density and the force acting in the radial direction ofthe tire is determined from a difference between the maximum value andthe minimum value of the variant pattern.
 4. A method for measuring atleast one of forces in a peripheral direction and a radial direction ofa running tire mounted onto a rim acted upon a around contact face, inwhich when a point on an outer peripheral face of the rim is Q and anintersect between a straight line passing through the point Q under noaction of external force and extending in the radial direction and aninner peripheral face of a tread portion of the tire is P, said forcesare determined from a variant pattern that a relative displacement ofthe point P to the point Q in the peripheral direction or the radialdirection is changed in accordance with a rotating position of the pointQ when the point P passes through the ground contact portion of thetire, wherein a magnetic field formed by a magnet arranged on one of thepoint P and the point Q is continuously measured by a magnetic sensorarranged on the other of the point P and the point Q, and the variantpattern of the relative displacement between the point P and the point Qis determined by reverse calculation from a variant pattern of amagnetic flux density changed in accordance with the relativedisplacement; wherein the measurement of the magnetic flux density iscarried out in parallel with respect to a pair of magnets arranged nearto each other so that changes of widthwise components of magnetic fluxdensities formed along the peripheral direction of the tire form areversal relation under no action of external force to the tire, andwhen an average value of maximum values in a reversal pattern reversedfrom a variant pattern of the magnetic flux density of the tirewidthwise component measured on one of the magnets and in a variantpattern of the magnetic flux density of the tire widthwise componentmeasured on the other magnet is an average maximum value and an averagevalue of minimum values in these patterns is an average minimum value,the force acting in the peripheral direction of the tire is determinedfrom an average between the average maximum value and the averageminimum value, and the force acting in the radial direction of the tireis determined from a difference between the average maximum value andthe average minimum value.
 5. An apparatus for measuring forces actedupon a tire according to any one of claim 1-4, wherein the magnet isconstituted with a sheet-shaped magnet having magnetic poles of the samepolarity at both ends in a longitudinal direction and a magnetic pole ofa polarity opposite to the magnetic poles of both the ends at a centerin the longitudinal direction, and the magnet is arranged so as toextend the longitudinal direction in a peripheral direction of the tire.6. An apparatus for measuring forces acted upon a tire according to anyone of claim 1-4, wherein the magnet is constituted with two magnetseach having magnetic poles of opposite polarities at both ends, andthese two magnets are extended in opposite directions to each other in awidthwise direction of the tire and arranged side by side in aperipheral direction of the tire.
 7. An apparatus for measuring forcesacted upon a tire, the apparatus comprising: a magnet arranged on aninner peripheral face of a tread portion; and a magnetic sensor attacheddirectly or indirectly through a fitting jig to an outer peripheral faceof a rim, wherein the magnet is arranged so that a magnetic force linedistribution of a magnetic field forms a plane symmetry with respect toa meridional plane of the tire including a point P or a point Q under noaction of external force to the tire, the magnet having magnetic polesof the same polarity at both ends in a longitudinal direction.
 8. Anapparatus for measuring forces acted upon a tire, the apparatuscomprising: a magnet arranged on an inner peripheral face of a treadportion; and a magnetic sensor attached directly or indirectly through afitting jig to an outer peripheral face of a rim, wherein a pair ofmagnets are arranged near to each other so that changes of widthwisecomponents of magnetic flux densities formed along a peripheraldirection of the tire form a reversal relation under no action ofexternal force to the tire.
 9. An apparatus for measuring forces actedupon a tire according to any one of claims 7 or 8, wherein the magnet isconstituted with at least one sheet-shaped magnet in which distributionsof magnetization at front and back faces thereof form a reversalrelation to each other.
 10. An apparatus for measuring forces acted upona tire according to claim 9, wherein the sheet-shaped magnet isconstituted with a rectangular rubber sheet of an even thickness inwhich the magnetization of the same polarity at each of the front andback faces is distributed substantially uniformly over a full facethereof.
 11. An apparatus for measuring forces acted upon a tireaccording to claim 10, wherein the sheet-shaped magnet is arranged so asto position a magnet center to the point P and direct a side of themagnet to a peripheral direction.
 12. An apparatus for measuring forcesacted upon a tire according to claim 10, wherein four rectangularsheet-shaped magnets having the same size are arranged so as to positiontheir magnet centers to apexes of a tetragon having a center at thepoint P and one side parallel to a peripheral direction of the tire, anda side of each of these magnets is directed to the peripheral directionof the tire, and distances separated between these magnets in theperipheral direction of the tire and the widthwise direction of the tireare not more than 100 mm, respectively, and directions of magnetic polesof the sheet-shaped magnets located at mutually adjacent apexes of thetetragon having a center at the point P are opposed to each other. 13.An apparatus for measuring forces acted upon a tire according to claim10, wherein two rectangular sheet-shaped magnets having the same sizeare arranged so as to position their magnet centers to a pair of apexesforming a diagonal relationship of a tetragon having a center at thepoint P and a side parallel to a peripheral direction of the tire, and aside of each of these magnets is directed to the peripheral direction ofthe tire, and distances separated between these magnets in theperipheral direction of the tire and the widthwise direction of the tireare not more than 100 mm, respectively, and directions of magnetic polesof these sheet-shaped magnets are made the same.
 14. An apparatus formeasuring forces acted upon a tire according to claim 10, wherein sixrectangular sheet-shaped magnets having the same size are arranged atthree rows from side to side along a peripheral direction of the tire inthe same direction and at equal intervals every two magnets, and a sideof each of these magnets is directed in the peripheral direction of thetire, and distances separated between these magnets in the peripheraldirection of the tire and in the widthwise direction of the tire are notmore than 100 mm, respectively, and directions of magnetic poles ofthese six magnets are opposed to each other even between the adjacentmagnets in the peripheral direction of the tire and in the widthwisedirection of the tire, and magnetic sensors are arranged on linespassing through centers of two rectangles formed by mutually adjacentfour sheet-shaped magnets under no action of external force to the tireand extending inward and outward in a radial direction in correspondenceto each of these rectangles.
 15. An apparatus for measuring forces actedupon a tire according to any one of claims 7 or 8, wherein the magnet orthe magnetic sensor is indirectly attached to an outer peripheral faceof a rim through a fitting jig and at a position separated outward fromthe outer peripheral face of the rim in a radial direction of the tire.16. An apparatus for measuring forces acted upon a tire according toclaim 15, which further comprises an adjusting means for adjusting adistance of the magnet or the magnetic sensor separated from the outerperipheral face of the rim, and an operating means for actuating theadjusting means arranged inward in the radial direction of the tire. 17.An apparatus for measuring forces acted upon a tire, the apparatuscomprising: a magnet arranged on an inner peripheral face of a treadportion; and a magnetic sensor attached directly or indirectly through afitting jig to an outer peripheral face of a rim, wherein the magnet isarranged so that a magnetic force line distribution of a magnetic fieldforms a plane symmetry with respect to a meridional plane of the tireincluding a point P or a point Q under no external force to the tire,the magnet having magnetic poles of the same polarity at both ends in alongitudinal direction.
 18. An apparatus for measuring forces acted upona tire, the apparatus comprising: a magnet attached directly orindirectly through a fitting jig to an outer peripheral face of a rim;and a magnetic sensor arranged on an inner peripheral face of a treadportion, wherein a pair of magnets are arranged near to each other sothat changes of widthwise components of magnetic flux densities formedalong a peripheral direction of the tire form a reversal relation underno action of external force to the tire.
 19. An apparatus for measuringforces acted upon a tire according to any one of claims 17 or 18,wherein the magnet or the magnetic sensor is indirectly attached to anouter peripheral face of a rim through a fitting jig and at a positionseparated outward from the outer peripheral face of the rim in a radialdirection of the tire.
 20. An apparatus for measuring forces acted upona tire according to claim 19, which further comprises an adjusting meansfor adjusting a distance of the magnet or the magnetic sensor separatedfrom the outer peripheral face of the rim, and an operating means foractuating the adjusting means arranged inward in the radial direction ofthe tire.